1. Field of the Invention
This invention relates, in general, to a voice analyzer apparatus and, more particularly, to a voice analyzer apparatus utilizing a residual excited linear predictive (RELP) coder that operates at 4800 BPS (bits per second) and is interoperable with a 2400 BPS system.
2. Description of the Background
Much work has been done in the area of human voice analyzing apparatuses. One of the more important developments for this is linear predictive coding (LPC). LPC is a mathematical procedure for estimating a filter function equivalent to the vocal tract. The estimate of the vocal tract resonance may be used to subtract vocal tract resonances from speech leaving an estimate of the excitation. The vocal tract function is estimated by removing correlation between a number of adjacent samples of the speech waveform, assuming that the wavefore may be modeled as an exponentially decaying sinusoid. A typical apparatus for providing the LPC correlation, excitation and amplitude information is disclosed in U.S. Pat. No. 4,378,469, issued to the inventor of the present invention and entitled "Human Voice Analyzing Apparatus".
Systems which operate at 2400 BPS provide, as vocal tract excitations, a unit pulse at certain intervals. This produces a sound that is of insufficient quality for commercial applications and has a mechanical tone to it.